Hi Thomas,
One important note to add. People who are upgrading from 2.5.x versions of Couchbase should consult MB-19635 to ensure they are moving to a version that supports offline upgrade from 2.5.x.
4.5.0 and 3.1.6 are safe choices. 4.1.2 has the fix but it hasn’t been released yet.
Best,
-Will